The present invention relates to a method of driving ramming parts under water in accordance with which a ramming device suspended on a supporting element and a submergible electrohydraulic drive unit are lowered under water, and the ramming device driven by the drive unit drives-in a ramming part. The invention deals also with a drive unit used for this method.
Excavation of raw deposits located on or under the sea bottom is performed with operations and by means of underwater arrangements and constructions which are arranged always in deep water. Therefore frequently ramming devices must be used in great water depths for driving-in of several ramming piles arranged at certain distances from one another. It is therefore always difficult to bring the ramming device on the ramming parts to be driven in with bearable time and labor expenses and to provide time and labor economical driving-in without damaging the ramming parts. Since for anchoring of offshore drilling platforms and similar structures many ramming piles of great diameter provided on their supporting legs must be rammed-in by respective heavy ramming devices with very high impact energy very deep into the sea bottom whose hardness increases with increasing depth, the ramming piles to be used often have to be dimensioned thicker and heavier than actually needed for the anchoring of the structure. This is needed for preventing bending damages to the ramming piles which have great length and are susceptible to bending forces, especially during the first phase of ramming-in, which can take place under high weight of several hundred tons of heavy ramming device, and also for preventing their deviation from the predetermined driving-in direction. Steel pipe piles which in practice often have several hundred meters and are provided with thick walls, are not only very expensive, but also heavy and dangerous to handle. The working ships therefore must be provided with high and thick derrick cranes.
For avoiding these difficulties, there have been utilized for ramming-in at relatively small water depths, relatively short ramming piles, which are then extended by additional pile portions which are welded to the driven-in piles above water. This, however, is not possible when ramming in great water depths.
For the utilization of narrower and thin-walled and therefore lighter ramming piles for ramming in great water depths, the ramming pile which extends freely from the sea bottom over a great length can only be pre-rammed with a light ramming device of a relatively low impact energy until no difficulties with their bending can be expected. Then the light ramming device must be withdrawn and a heavier ramming device is lowered onto the ramming pile to ram the same to the predetermined insertion depth. In this operation, however, two different ramming devices must be placed on the same ramming pile one after the other and withdrawn above water. In unfavorable weather conditions during offshore works this takes too much time and requires high expenses because of enormous costs of modern work ship. This is especially true when the ramming must be performed in such water depths in which driving of the ramming device by pressure fluid which is supplied from a base above water is no longer possible because of the high pressure losses of long hose conduits and/or too high viscosity increase of the pressure fluid in cold sea water. In these cases each ramming device must be lowered with a correspondingly designed submergible electrohydraulic drive unit to the working depth, so that not only two different ramming devices, but also additionally two respective driving units must be made available and handled.